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In cell biology, microtubule nucleation is the event that initiates de novo formation of microtubules (MTs). These filaments of the cytoskeleton typically form through polymerization of α- and β-tubulin dimers, the basic building blocks of the microtubule, which initially interact to nucleate a seed from which the filament elongates.
Microtubule and tubulin metrics [1]. Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm [2] and have an inner diameter between 11 and 15 nm. [3]
Microtubule polymerization is nucleated at the microtubule organizing center. An aster is a cellular structure shaped like a star , consisting of a centrosome and its associated microtubules during the early stages of mitosis in an animal cell.
Centrosome reduction is the gradual loss of centrosomal components that takes place after mitosis and during differentiation [22] In cycling cells, after mitosis the centrosome has lost most of its pericentriolar material (PCM) and its microtubule nucleation capacity.
The growing ends of microtubules are shown in green (labeled with green fluorescent protein fused to the microtubule plus end binding protein EB1 of Arabidopsis thaliana). N = Nucleus, V = Vacuole, PPB = Preprophase band, MTN = Microtubule nucleation starts at the nuclear envelope, NEB = Nuclear envelope breakdown at the onset of prometaphase .
However, these two motifs are not the only essential ones in microtubule branching nucleation; the FKARP motifs of α5 and α6 are also essential for stimulating this process. [11] Furthermore, the α-helical region stretch of domain α7 and the C-terminal residues that interact with Eg5 are critical for microtubule branching nucleation as well ...
The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus , which separate the chromosomes during cell division .
The PCM contains proteins responsible for microtubule nucleation and anchoring [9] — including γ-tubulin, pericentrin and ninein. In general, each centriole of the centrosome is based on a nine-triplet microtubule assembled in a cartwheel structure, and contains centrin, cenexin and tektin. [10]